Abstract: A support jack, in particular for supporting semitrailers, includes a vertically telescopically displaceable supporting element having an outer sleeve, and an inner sleeve that can be vertically displaced in a telescopic fashion, each sleeve having a rectangular cross-section with four sidewalls. At least the inner sleeve has a wall plate joined to two adjacent side walls with welding seams that improve the bending stiffness of the support jack. The welding seams can be located inside or outside either of the sleeves. Such a support jack can be located on the lower side of any vehicle.